Hydrophobic/oleophobic fabrics with directional liquid transport property

ABSTRACT

Described are fabrics and articles of manufacture. Also described are methods of making the fabrics. A fabric may exhibit directional liquid transport. The fabrics have a plurality of domains. A domain may connect a first side of the fabric and a second side of the fabric that is opposite the first side. The plurality of domains may have a gradient in concentration of hydrophobic and/or oleophobic groups. The fabrics may include nanoparticles. The fabrics may be made by exposing selected areas of a superhydrophobic and/or oleophobic fabric to an oxygen or air plasma.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/750,062, filed on Oct. 24, 2018, the disclosure of which is herebyincorporated by reference.

BACKGROUND OF THE DISCLOSURE

Clothing provides a microclimate between the body and the externalenvironment, and acts as a barrier for heat and vapor transfer inbetween. There are various functional requirements for textile orfibrous systems for different clothing applications. In particular, thehuge demand of sportswear and sports equipment has raised up developmentof new technologies with better functional properties. Generally, thesportswear clothing system has specific features that can be modulatedusing the properties of the constituent materials (fiber, yarn andfabric), of which, thermal comfort including moisture and liquidtransport properties is a critical requirement. For instance, insweating conditions under active sports, the fibrous system next to theskin should not absorb sweat (water), instead, it has to transport sweat(water) through the fabric promptly to avoid the discomfort of thefabric sticking to the skin. On the other hand, it is desirable to havethe side of the fabric exposed to the external environment to beomni-repellent so as to protect rain, stains and liquid pathogen.Therefore, there is a high demand to design fabric materials that havedirectional water transport (also referred as “one-way” water transport)property, i.e. directionally transport water from the skin to theenvironment, but minimize the transport in the reverse direction (fromthe environment to the skin).

Recently, two major strategies have been reported to endow the fibrousmaterials with directional liquid transport properties. One is to createlyophilicity (e.g. hydrophilicity or oleophilicity) gradient through thefabric thickness, another one is to assemble two layers of materialswith different lyophilicity as an asymmetric construct. In both cases,liquid tends to transport from lyophobic (e.g. hydrophobic oroleophobic) side to lyophobilic (e.g. hydrophilic or oleophilic) side ofthe fibrous materials, but is blocked in the reverse direction. Forinstance, for the first case, Wang et al., Kong et al. and Zhou et al.separately applied photo-sensitive superhydrophobic coating on cotton orpolyester fabrics followed by UV illumination on one-side to inducehydrophilicity gradient to enable directional water transport abilitiesthrough the fabric thickness. Zhang et al. preparedhydrophilic-to-hydrophobic gradient dynamers via phase separation andused them as asymmetric membranes for directional water transport. Forthe second case, Wu et al. and Wang et al. used electrospinning to formhydrophobic/hydrophilic and oleophobic/oleophilic dual-layer nanofibrousmembrane with directional water and oil transport properties,respectively. Tian et al. used vapor diffusion method to depositfluoroalkyl silane on one side of cotton fabric to formhydrophilic/hydrophobic Janus-type membrane with directional waterdroplet gating behavior. Sun et al. used three-step plasmapolymerization to create asymmetric wettability on bifacial fabrics todevelop directional water transport ability. Zeng et al., Liu et al. andWang et al. similarly electrosprayed a thin layer of hydrophobic coatingon a hydrophilic fabric to endow the directional water transportability. Yang et al. and Si et al. similarly treated hydrophobicmembranes by floating one side on the hydrophilic solution to form Janusmembranes with directional water penetration ability.

Although, in these current designs, liquid (e.g. water) is able todirectionally transport from the hydrophobic side to the hydrophilicside of the fabrics or membranes, but not vice versa, liquid tends tospread and be absorbed on the hydrophilic side. Consequently, thedirectional water transport will stop when the hydrophilic side is fullysaturated and the saturation of water on the hydrophilic side may alsoincrease discomfort due to increased weight. In addition, thehydrophilic external side of the fabric make it non-preventive toexternal water, stain or liquid pathogen. A desirable situation for asmart sportswear is to mimic the behavior of human skin. Human skin is adesirable directional liquid transport material as it excretes liquidsweat and protect the body from external liquid contaminants. In adesirable “skin-like” directional liquid transport fabric, water (e.g.,sweat) can not only transport from the water-source, e.g., skin side, tothe environment side and keep the skin side dry, it can also transportthrough to the external side for evaporation, which results in cooling,and any extra sweat will be rolled off from the external side of thefabric; meanwhile, water (e.g., rain, liquid stain, or pathogen) willnot transport from the external side to the skin side, neither will itbe absorbed on the outer layer facing the environment.

Based on the foregoing, there exists an ongoing and unmet need forfabrics having desirable directional liquid transport and/or waterrepellent properties.

SUMMARY OF THE DISCLOSURE

The present disclosure provides fabrics. The present disclosure alsoprovides methods of making fabrics and uses thereof.

In this disclosure, a directional water transportable hydrophobic fabricby, for example, a selective plasma treatment via patterned mask tocreate gradient wettability channels through the fabric thickness. Thegradient wettability was confirmed by chemical analysis, wherehydrophobic chains were found etched away by plasma selective treatment.The directional water transport property was confirmed via variousmeasurements, such as, for example, contact angle test, water drippingtest, shower test as well as water flux test, where water was found tobe directionally transported from a hydrophobic surface to a lesshydrophobic surface or a hydrophilic surface through the spot channelsacross the fabric thickness, while non-treated surfaces on both sidesremained hydrophobic. The technology can be readily extended for othermembranes as well as directional flow of other types of liquid, such asoils.

In an aspect, the present disclosure provides fabrics. The fabricscomprise a plurality of domains (e.g., channels, pores, and the like),connecting (e.g., in fluid communication with) a first side of thefabric (e.g., superhydrophobic fabric, oleophobic fabric, and the like)and a second side of the fabric (e.g., superhydrophobic fabric,oleophobic fabric, and the like) opposite the first side.

In an aspect, the present disclosure provides methods of making fabrics.The fabrics may be fabrics of the present disclosure. In variousexamples, a fabric (e.g., a fabric of the present disclosure) is made bya method of the present disclosure. In various examples, the methods useselective formation (e.g., using masking and selective treatment) of afabric to form domains exhibiting directional liquid (e.g., water and/oroil) transport. Non-limiting examples of methods of making fabrics aredescribed herein.

In an aspect, the present disclosure provides uses of fabrics.Non-limiting examples of uses of fabrics of the present disclosure aredescribed herein.

BRIEF DESCRIPTION OF THE FIGURES

For a fuller understanding of the nature and objects of the disclosure,reference should be made to the following detailed description taken inconjunction with the accompanying figures.

FIG. 1 shows a design of a hydrophobic fabric with gradient wettabilitychannels through the fabric thickness to enable directional watertransport property.

FIG. 2 shows water droplet images taken from contact angle measurementon horizontally laid superhydrophobic finished cotton fabric afterplasma selective treatment under 300 W for 3 min. ((a1), (b1)) Typicaldroplet motion on (a1) exposed top spot and (b1) unexposed back spotareas of the fabric for 3 s, respectively. ((a2), (b2)) Typical dropletimages on both spot and non-spot areas of the (a2) top side and (b2)back side of the fabric, respectively.

FIG. 3 shows still frames taken from videos when water was dripped onthe inclinedly laid (an angle of 45°) plasma selectively treated (300 W,3 min) superhydrophobic finished cotton fabric, on (a1) exposed topspots (time interval, 0.25 s) and (b1) unexposed back spots (timeinterval, 1.00 s), respectively. Spots on the fabrics indicate theexposed top spots. Arrows in the last images indicate final wateradhesion only on exposed top spots.

FIG. 4 shows a schematic design and fabrication process of a “skin-like”hydrophobic fabric with both directional water transport and waterrepellent properties. (A) Schematic demonstration of the dual propertiesof the “skin-like” fabric. (B) A combination of superhydrophobicfinishing via perfluorosilane-coated titanium dioxide (TiO₂)nanoparticles and selective plasma treatment via a patterned mask tocreate gradient wettability spot channels through the fabric thicknessto endow the dual properties.

FIG. 5 shows wetting behavior, microstructure, and chemical analysis ofthe superhydrophobic finished fabric after selective plasma treatment.(A) Contact angles of the spot and non-spot areas of both top and backsides of the superhydrophobic finished fabric after plasma treatment for0 to 5 min; insets are droplet images when dripped on the back spotareas. (B) Contact angle of a two-layer fabric assembly to prove thewettability gradient. (C) SEM morphologies of pristine cotton fabric,superhydrophobic finished fabric, and exposed top spot areas of thesuperhydrophobic finished fabric after selective plasma treatment for 3and 5 min. (D) Table of atomic contents of C, O, Ti, Si and F ondifferent fabric surfaces from X-ray photoelectron spectroscopy (XPS)results.

FIG. 6 shows directional water transport properties and water repellencyof the superhydrophobic finished fabric after selective plasmatreatment. (A) Still frames taken from videos when water was drippedonto an inclinedly laid (45°) plasma selectively treatedsuperhydrophobic finished fabric on exposed top spot and unexposed backspot areas under a flow rate of 10 μL/min. (B, C) Breakthrough pressuresof both top and back sides of the fabrics with (B) different sizes(diameters) of spot areas under a flow rate of 0.4 mL/min and (C)different flow rates through a spot diameter of 1 mm, respectively.

FIG. 7 shows a mechanism of directional water transport. (A)Illustration of directional water transport through the spot channelbetween elliptical yarns with gradient wettability. (B) Illustration ofan axisymmetric water fluid front between elliptical yarns. Here, a andb are the semi-principal axes in x- and y-directions, respectively, c isthe half distance between yarns, θ is the contact angle, co is theeccentric anomaly, a is the expansion/contraction angle, and β is thedirection angle. (C) Dependence of direction angle on the eccentricanomaly of the elliptical yarns in different flow directions. (D)Dependence of capillary pressure on the eccentric anomaly of theelliptical yarns in different flow directions. (E) Mechanical analysisof the water drop hung under the porous spot of the horizontally placedfibrous layer with increasing water supply. (F) Relationship between thesize of the porous spot and the volume of the dripped water drop. (G)Mechanical analysis of the water drop attached on the porous spot of theinclined fibrous layer at an incline angle of λ.

FIG. 8 shows water droplet images (from contact angle test) on pristinecotton fabric, and both spot areas and non-spot areas from both top andback sides of the superhydrophobic finished fabric before and afterselective plasma treatment for 1 to 5 min.

FIG. 9 shows water droplet images taken from contact angle measurementon a horizontally laid superhydrophobic finished fabric after plasmaselective treatment (300 W, 3 min). (A, B) Typical droplet motion on (A)exposed top spot and (B) unexposed back spot areas of the fabric for 3s, respectively. (C, D) Typical droplet images on both spot and non-spotareas of the (C) top side and (D) back side of the fabric, respectively.

FIG. 10 shows wetting durability of the superhydrophobic finished fabricafter selective plasma treatment. (A) Contact angles of the spot andnon-spot areas of both top and back sides of the superhydrophobicfinished fabric after plasma treatment for 0 to 5 min after 7 days;insets are droplet images when dripped on the back spot areas. (B) Watertransport time from the back spot area to the top spot area in both Day0 (as-prepared) and Day 7. (C) Overview images of multiple waterdroplets on either side of the superhydrophobic finished fabric afterselective plasma treatment (300 W, 3 min), at Day 0 and Day 7. Arrowsindicate the spot channels marked in black dots on the fabrics. Insetsin as-prepared samples are side views of the fabrics and droplets.

FIG. 11 shows SEM morphologies of exposed top spot areas and unexposedback spot areas of the of the superhydrophobic finished fabric afterselective plasma treatment for 1 to 10 min. Images in Line 2 and 4 arehigh magnifications of Line 1 and 3, respectively.

FIG. 12 shows SEM morphologies of unexposed top and back non-spot of thesuperhydrophobic finished fabric after selective plasma treatment for 1to 10 min. Images in Line 2 and 4 are high magnifications of Line 1 and3, respectively.

FIG. 13 shows thermogravimetric analysis (TGA) spectra of pristinecotton fabric, superhydrophobic finished fabric before and after plasmatreatment (300 W, 3 min).

FIG. 14 shows (A) experimental set-up for measuring breakthroughpressure of the fabrics. (B) Water droplet diameters transported throughdifferent sizes (diameters) of spot areas under a flow rate of 0.4mL/min.

FIG. 15 shows (A) a water shower test to measure the water transportthrough the different sides of the plasma selectively treatedsuperhydrophobic finished fabric. Water (B) did not and (C) didtransport (arrow) through the fabric at 10 s when (B) the top side and(C) back side of the fabric were up contacting the shower, respectively.

FIG. 16 shows SEM morphologies of (A) cross-section of thesuperhydrophobic finished cotton fabric, showing the semi-axes a and bof the yarn are approximately 80 μm and 50 μm, respectively, and (B) lowmagnification of images in FIG. 5C, showing a half distance capproximately 50 μm and a big pore with greater c (arrow) between yarnsof the superhydrophobic finished fabric.

FIG. 17 shows dependence of direction angle on eccentric anomaly of theelliptical yarns in different flow directions. The semi-major axis andsemi-minor axis vary at different values of the maximum contact angleson one side of the porous spot.

FIG. 18 shows dependence of capillary pressure on eccentric anomaly ofthe elliptical yarns: (A) at different semi-principal axes in differentflow directions. The semi-principal axes and the half-distance betweenyarns vary in three groups as follows: a=80 μm, b=50 μm, c=50 μm; a=80μm, b=50 μm, c=100 μm; and a=160 μm, b=100 μm, c=100 μm. (B) atdifferent shapes of elliptical yarns in different flow directions. Thesemi-principal axes and vary in three groups as follows: a=40 μm, b=50μm; a=80 μm, b=50 μm; and a=160 μm, b=50 μm. (C) at different maximumcontact angles in different flow directions. The contact angles vary inthree groups as follows: θ₀=109°; θ₀=130°; and θ₀=150°.

DETAILED DESCRIPTION OF THE DISCLOSURE

Although claimed subject matter will be described in terms of certainembodiments and examples, other embodiments and examples, includingembodiments and examples that do not provide all of the benefits andfeatures set forth herein, are also within the scope of this disclosure.Various structural, logical, and process step changes may be madewithout departing from the scope of the disclosure.

Ranges of values are disclosed herein. The ranges set out a lower limitvalue and an upper limit value. Unless otherwise stated, the rangesinclude the lower limit value, the upper limit value, and all valuesbetween the lower limit value and the upper limit value, including, butnot limited to, all values to the magnitude of the smallest value(either the lower limit value or the upper limit value).

The present disclosure provides fabrics. The present disclosure alsoprovides methods of making fabrics and uses thereof.

In this disclosure, a directional water transportable hydrophobic fabricby, for example, a selective plasma treatment via patterned mask tocreate gradient wettability channels through the fabric thickness. Thegradient wettability was confirmed by chemical analysis, wherehydrophobic chains were found etched away by plasma selective treatment.The directional water transport property was confirmed via variousmeasurements, such as, for example, contact angle test, water drippingtest, shower test as well as water flux test, where water was found tobe directionally transported from a hydrophobic surface to a lesshydrophobic surface or a hydrophilic surface through the spot channelsacross the fabric thickness, while non-treated surfaces on both sidesremained hydrophobic. The technology can be readily extended for othermembranes as well as directional flow of other types of liquid, such asoils.

In an aspect, the present disclosure provides fabrics. The fabricscomprise a plurality of domains (e.g., channels, pores, and the like),connecting (e.g., in fluid communication with) a first side of thefabric (e.g., superhydrophobic fabric, oleophobic fabric, and the like)and a second side of the fabric (e.g., superhydrophobic fabric,oleophobic fabric, and the like) opposite the first side.

In various examples, the fabric (e.g., superhydrophobic fabric,oleophobic fabric, and the like) comprises a plurality of hydrophilicand/or oleophilic domains, which may be non-randomly distributed (e.g.,distributed in a non-random pattern). The fabrics may exhibitdirectional liquid transport. In various examples, a fabric disclosedherein exhibits a gradient property, such as, for example, thedirectional liquid (such as, for example, water, sweat, oil, such as,for example, oily compounds or mixtures of such compounds, and the like,and combinations thereof) transport for the inner layer and waterrepellent properties for the outer layer. Non-limiting examples offabrics are described herein.

In an example, a fabric of the present disclosure provides 1) acontinuous hydrophobic nature, which may result from gradientwettability domains (which may be referred to as channels), and/or 2) anoverall superhydrophobic surface.

In various examples, the hydrophilic domains account for 0.1-75 mol % orwt % (e.g., 0.5-50 mol % or wt %) of the surface area of the fabric,including all 0.1% values and ranges therebetween.

The plurality of domains may have a variety of shapes. The shapes may becross-sectional shapes. Examples of shapes include, but are not limitedto, round shape, rectangular, oval, kidney shaped, triangular, starshaped, and the like, and combinations thereof.

Each of the plurality of domains has a size. In various examples, eachof the plurality of domains has a size (e.g., one or more dimension(s))of, individually, 100 microns to 5 mm, including all integer micronvalues and ranges therebetween. In various examples, each of theplurality of domains has a size (e.g., one or more dimension) of,individually, 500 microns to 3 mm. Each domain may be the same size,each domain may have a different size, or at least one of the domains ofthe plurality of the domains has a size that is different from at leastone other domain of the plurality of domains.

A fabric of the present disclosure may comprise or be a fabric, whichmay be a hydrophobic fabric, comprising or made of natural fibers (e.g.,cotton, flax, jute, wool, silk, linen, and the like), or syntheticfibers (e.g., polyester, nylon, polyolefin, acrylic, acetate,polyurethane, and the like), or semi-synthetic fibers (e.g. rayon,viscose, and the like), or a combination thereof. These fabrics may havea structure, including, but not limited to, a knitted fabric, a wovenfabric, a non-woven fabric, and the like.

A fabric of the present disclosure may be characterized by a gradient inhydrophilicity (e.g., from hydrophobic character to hydrophiliccharacter) and/or oleophobicity (e.g., from oleophobic character tooleophilic character) of (e.g., within) the plurality of domains along adirection from the first side (e.g., an interior side) to the secondside (e.g., an exterior side) of the fabric (e.g., a superhydrophobicfabric, oleophobic fabric, and the like).

The gradient in hydrophilicity (e.g., from hydrophobic character tohydrophilic character) and/or oleophilicity (e.g., from oleophobiccharacter to oleophilic character) results from a gradient inconcentration of hydrophobic and/or oleophobic groups (e.g., fluoroalkylgroups, such as, for example, perfluoroalkyl groups, and the like; alkylgroups, such as, for example, propyl groups, and the like;silsesquioxane groups, such as, for example, polyoctahedralsilsesquioxanes (POSS), and the like; and siloxane groups, such as, forexample, polydimethylsiloxane (PDMS), and the like)) and, optionally, aplurality of nanoparticles and/or disposed on one or more (e.g., both)fabric surface(s) (e.g., the first side and/or second side of a fabric)and/or through at least a portion or all of a thickness of the fabric(e.g., to one or more fiber of the fabric). In various examples, thehydrophobic and/or oleophobic groups account for 1-10, 1-25, 1-50, 1-75,or 1-100 (e.g., 10-50, 10-75, or 10-100) mol % or wt % (based on thetotal weight of the fabric), including all 0.1 mol % or wt % values andranges therebetween, of the fabric and/or the nanoparticles account for1-50 (e.g., 1-20) wt % (based on the total weight of the fabric),including all 0.1 wt % values and ranges therebetween, of the fabric. Invarious other examples, the hydrophobic and/or oleophobic groups accountfor 1-100 (e.g., 10-100) wt % (where the weight percentage is therelative weight of hydrophobic and/or oleophobic groups to the weight ofthe fabric, for example, the weight of hydrophobic and/or oleophobicgroups divided by the weight of the fabric multiplied by 100), includingall 0.1 wt % values and ranges therebetween, of the fabric and/or thenanoparticles account for 1-50 (e.g., 1-20) wt % (based on the totalweight of the fabric), including all 0.1 wt % values and rangestherebetween, of the fabric.

A plurality of nanoparticles (or at least a portion of thenanoparticles) may have a plurality of superhydrophobic groups (e.g.,fluoroalkyl groups, such as, for example, perfluoroalkyl groups, and thelike) covalently bound to a surface of the nanoparticles. Thenanoparticles may be superhydrophobically-modified nanoparticles.Non-limiting examples of superhydrophobically-modified nanoparticlesinclude fluorosilane-modified nanoparticles (such as, for example,fluorosilane-modified titania nanoparticles).

In various examples, hydrophobic and/or oleophobic groups (e.g.,fluoroalkyl groups such as, for example, perfluoroalkyl groups) areconnected to the fabric surface (e.g., to one or more fiber of thefabric) via one or more covalent bonds (e.g., —O—Si(—R)—O— moieties,where R is a hydrophobic group or an oleophobic group). The hydrophobicand/or oleophobic groups may be formed from (e.g., result from reactionof) one or more compound(s) and/or polymer(s), which may be inorganicpolymers or organic polymers, comprising hydrophobic and/or oleophobicgroups. In various examples, hydrophobic and/or oleophobic groups areformed from/using polyolefins, such as, for example, polypropylene, andthe like, waxes, such as, for example, paraffin wax, and the like. Invarious examples, fluoroalkyl groups are formed from (e.g., result fromreaction of) precursor compounds, such as, for example,¹H,¹H,²H,²H-perfluorooctyltriethoxysilane (PFOTES),¹H,¹H,²H,²H-perfluorodecyltrichlorosilane (PFTDS),¹H,¹H-perfluorooctylamine (PFOTA), perfluorooctylated quaternaryammonium silane coupling agent (PFSC),¹H,¹H,²H,²H-perfluorooctyltrichlorosilane (PFOTS),poly(tetrafluoroethylene) (PTFE),¹H,¹H,²H,²H-perfluorodecyltrichlorosilane (PFODS),¹H,¹H,²H-perfluoro-1-dodecene (PFDDE),(heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane (FDTS),perfluoroalkyl methacrylic copolymer (PMC), and the like, andcombinations thereof. The fluoroalkyl groups (e.g., perfluorinated alkylgroups) may be connected to the surface via one or more covalent bonds.

In various examples, the plurality of nanoparticles are chosen fromtitania nanoparticles, silica nanoparticles, zinc oxide nanoparticles,carbon nanoparticles (which may be carbon nanotubes), and the like, andcombinations thereof. The nanoparticles may have a size (e.g., longestdimension) of 1 nm to 1 micron (e.g., 5 nm to 1 micron), including allinteger nm values and ranges therebetween.

In an aspect, the present disclosure provides methods of making fabrics.The fabrics may be fabrics of the present disclosure. In variousexamples, a fabric (e.g., a fabric of the present disclosure) is made bya method of the present disclosure. In various examples, the methods useselective formation (e.g., using masking and selective treatment) of afabric to form domains exhibiting directional liquid (e.g., water,sweat, oil, such as, for example, oily compounds or mixtures of suchcompounds, and the like, and combinations thereof) transport.Non-limiting examples of methods of making fabrics are described herein.

The fabrics, which may be hydrophobic fabrics, may be made of naturalfibers (e.g., cotton, flax, jute, wool, silk, linen, and the like),synthetic fibers (e.g., polyester, nylon, viscose, polyolefin, acrylic,acetate, polyurethane, and the like), semi-synthetic fibers (e.g.,rayon, viscose, and the like), or the like, or a combination thereof. Invarious examples, a fabric is chosen from cotton fabrics, polyesterfabrics, nylon fabrics, viscose fabrics, polyurethane fabrics, andcombinations thereof.

In various examples, a method of forming a fabric (e.g.,superhydrophobic and/or oleophobic fabric, and the like) exhibitingdirectional liquid (e.g., water, sweat, oil, such as, for example, oilycompounds or mixtures of such compounds, and the like, and combinationsthereof) transport (e.g., a superhydrophobic and/or oleophobic fabric),the method comprising: exposing selected areas (e.g., selected areas ofone side) of a superhydrophobic and/or oleophobic fabric to an oxygen orair plasma (e.g., using a mask), chemical etching (e.g. sodiumhydroxide), or chemical deposition (e.g., fluorochemicals), such thatone or more domains exhibiting a water (e.g., wettability), sweat, oil,such as, for example, oily compounds or mixtures of such compounds, andthe like, and combinations thereof transport gradient from a first sideof the fabric to the second side of the fabric opposite the first sideof the fabric are formed, where the superhydrophobic and/or oleophobicfabric exhibiting directional liquid (e.g., water and/or oil) transportis formed. For example, the method is carried out at room temperatureand ambient/unaltered atmospheric conditions.

In various examples, the exposing selected areas of the superhydrophobicand/or oleophobic fabric to a plasma (e.g. oxygen plasma, air plasma,and the like) or UV luminance, chemical etching (e.g. sodium hydroxide),chemical deposition (e.g., fluorochemicals) is carried out using amasking material (e.g., a paper tape mask, hot melt film mask,impermeable lining film, water-based adhesive or resist (e.g. glue) toform a mask film, and the like) having a plurality of apertures, theapertures corresponding to the selected areas (e.g., plurality ofdomains). For example, the plasma conditions are 50-500 W, including allinteger W values and ranges therebetween, and/or treatment time of 30 s(s=second(s)) to 30 min (min=minute(s)) (e.g., 30 s to 10 min),including all integer second values and ranges therebetween (e.g., theplasma power is 100-300 W and treatment time is 1-15 min (e.g., 1-5 min)(shorter time may be desirable if the power is higher)).

In various examples, a superhydrophobic and/or oleophobic fabric isformed by: contacting a fabric (e.g., a hydrophilic and/or oleophilicfabric) with: i) one or more hydrophobic group precursor (e.g.,fluoroalkyltrialkoxysilane(s)) and/or one or more oleophobic groupprecursor (e.g., fluoroalkyltrialkoxysilane(s)), ii) optionally,nanoparticles, ii) optionally, a solvent (e.g., ethanol, propanol,acetone, dimethyl formamide (DMF), and the like, and combinationsthereof) to form a superhydrophobic and/or oleophobic fabric.

Fabrics prepared by a method of the present disclosure may have ahydrophobic and/or oleophobic coating (e.g., the fabric is subjected toa hydrophobic and/or oleophobic finishing process). A finishing processmay comprise contacting the fabric with a plurality of nanoparticles andthe like. For example, in the case of a hydrophilic and/or oleophilicfabric, subjecting the hydrophilic and/or oleophilic fabric to a process(e.g., a pre-finishing process) may provide a hydrophobic and/oroleophobic fabric. Examples of suitable processes for rendering ahydrophilic fabric hydrophobic are known in the art.

In various examples, the one or more hydrophobic group precursors and/orone or more oleophobic group precursors, optionally the plurality ofnanoparticles, and optionally the solvent are present as a preformedmixture. For example, the one or more hydrophobic and/or oleophobicprecursors comprise 1-100 (e.g., 10-100) mol % or wt % based on thetotal weight of the fabric, including all 0.1% values and rangestherebetween, and/or the plurality of nanoparticles comprise 1-50 (e.g.,1-20) wt % based on the total weight of the fabric, including all 0.1%values and ranges therebetween.

Various hydrophobic group precursors may be used in a method of thepresent disclosure. For example, fluoroalkyltrialkoxysilane groups areused. Non-limiting examples of fluoroalkyltrialkoxysilane groups include¹H,¹H,²H,²H-perfluorooctyltriethoxysilane (PFOTES),¹H,¹H,²H,²H-perfluorodecyltrichlorosilane (PFTDS),¹H,¹H-perfluorooctylamine (PFOTA), perfluorooctylated quaternaryammonium silane coupling agent (PFSC),¹H,¹H,²H,²H-perfluorooctyltrichlorosilane (PFOTS),poly(tetrafluoroethylene) (PTFE),¹H,¹H,²H,²H-perfluorodecyltrichlorosilane (PFODS),¹H,¹H,²H-perfluoro-1-dodecene (PFDDE),(heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane (FDTS),perfluoroalkyl methacrylic copolymer (PMC), and the like, andcombinations thereof.

Various nanoparticles may be used in a method of the present disclosure.Examples of nanoparticles include, but are not limited to, titaniananoparticles, silica nanoparticles, zinc oxide nanoparticles, carbonnanoparticles (which may be carbon nanotubes), and the like, andcombinations thereof. The nanoparticles may have a size (e.g., longestdimension) of 1 nm to 1 micron (e.g., 5 nm to 1 micron), including allinteger nm values and ranges therebetween.

In an aspect, the present disclosure provides uses of the fabrics.Non-limiting examples of uses of the fabrics of the present disclosureare described herein.

An article of manufacture may be an article of clothing. The article ofclothing may be a breathable article of clothing. For example, thearticle of clothing is rainwear, outdoor clothing, sportswear, skiwear,hiking wear, underwear, or the like. The article of clothing may be ajacket, pants, or the like.

In various examples, articles of manufacture may comprise fabrics of thepresent disclosure. An article of manufacture may be a wearable article,such as, for example, an article of clothing (e.g., a waterproof oroil-proof article of clothing). In various examples, wearable articlesinclude, but are not limited to, rainwear, outerwear, outdoor clothing,sportswear, skiwear, hiking wear, under garments (e.g., underwear,undershirt, and the like), socks, t-shirts, hats, gloves, mittens,jackets, coats, ponchos, or the like. The articles of manufacture may bean article of outdoor equipment article. In various examples, outdoorequipment article is a tent, an awning, a tarp, a sleeping bag, or thelike.

The steps of the method described in the various embodiments andexamples disclosed herein are sufficient to produce a fabric of thepresent disclosure. Thus, in an embodiment, a method consistsessentially of a combination of the steps of the methods disclosedherein. In another embodiment, a method consists of such steps.

The following examples are presented to illustrate the presentdisclosure. The examples are not intended to be limiting in any matter.

Example 1

This example provides examples of fabrics of the present disclosure,characterization of same, methods of making same, and uses of same.

Asymmetric wettability channels were created on a hydrophobic fabric toenable directional water transport properties. A combination ofsuperhydrophobic finishing via fluorosilane-coated titanium dioxide(TiO₂) nanoparticles and selective plasma treatment via patterned maskwere used to create gradient wettability channels through the cottonfabric thickness (FIG. 1). While these channels are served fordirectional water transport, the untreated larger surface remainedsuperhydrophobic, therefore still provide water-repellent properties andthermal comfort next to the environment and the skin, respectively, whenthe fabric is used as a textile material.

The water transport ability was confirmed via various measurements, suchas contact angle test, water dripping test, shower test as well as waterflux test. For instance, FIG. 2(a 1), 2(b 1) shows a series of typicalimages taken from contact angle video when 10 μL water droplet wasplaced on top and back spot areas of the plasma (300 W, 3 minutes (min))selectively treated superhydrophobic finished cotton fabric,respectively. When water was dropped onto the top spot area, the dropletstayed on the surface steadily for 3 seconds (s) (FIG. 2(a 1)) andlonger time (not shown), with an average contact angle (CA) of 97°.However, when it was dropped on the back spot area, the droplet quicklytransported through to the other side (top side) of the fabric (FIG. 2(b1)). This difference indicates the directional water transport abilityof the plasma selectively treated fabric through the spot channels fromback to top side.

While the phenomena of directional water transport looks similarly atthe first glance as those reported in prior studies, our technologydiffers from them in two advantages, 1) the continuous hydrophobicnature on the top spot, and/or 2) an overall superhydrophobic surface onother non-spot areas. To be more specific, firstly, the as-showed topspot area (plasma treated under 300 W, for 3 min) has an average CA of97° and did not change within 3 s and longer time (FIG. 2(a 1)), whilethat of the fabrics in prior studies was zero within 3 s and quicklyspread to surrounding areas. Secondly, the unexposed non-spot areas onboth top and back sides of the as-prepared fabric were stillsuperhydrophobic, shown as two still round droplets at both sides of thetop and back spots (FIG. 2(a 2), 2(b 2)), with average CA over 140°,while the surface of the fabrics in prior studies had no selectivity inthe hydrophilicity on the same side, i.e. the surface was eitherhydrophilic or hydrophobic.

These two advantages of our technology were further validated by anotherwater transport test, where the fabrics were placed inclinedly with anangle of 45°, and water was dripped from either top or back spot areasof the fabric. FIGS. 2(a 1)-2(b 2) shows a series of photos taken fromvideos during these experiments. When water was dripped from top side ofthe fabric, it tended to roll off from the fabric very quickly (FIG.3(a)); no transport was observed during this process. On the reservedirection, water tended to transport to the top side when being suppliedfrom the back spot areas, and roll off again after accumulating to alarge droplet (FIG. 3b )). For both cases, most of water has rolled offfrom the top side of the fabric, with only slightly adhesion on the spotarea (arrow of last images in FIGS. 3(a), 3(b)). While the directionalwater transport property was further proved in this test, the roll-offability of water droplets indicates the water repellency of the fabric,which is clearly due to the superhydrophobicity of the non-spot areas ofthe both surfaces.

The design of selective hydrophilicity gradient across the fabricthickness enabled directional water transport occurs only in the spotchannel areas, while the hydrophobic nature of the other larger areaswill provide the water repellency for the fabric and thereafter thermalcomfort for the clothing application. The technology is applicable forall kinds of fabrics. For hydrophilic fabrics, as in the example ofcotton fabric, one needs to first make it hydrophobic, such aspre-finishing, and then make the hydrophilic gradient channels; forhydrophobic fabrics, this pretreatment is not necessary. A desirablepercentage of the hydrophilic areas on the external side providesdirectional water transport, i.e. if the percentage is too small, itwill not transport water effectively and reduce the water evaporationarea for evaporative cooling, while too large, the water droplets willnot fall off. Either the hydrophobic pre-finishing or plasma selectivetreatment is simple, cost-effective and efficient, therefore will bevery feasible for the commercial applications.

This technology can be used to provide a directional water transportablehydrophobic fabric. It has a high significance to the apparel industryto provide the clothing systems, particularly sportswear, with bothdirectional water property and water repellency, therefore would bring ahuge value for the industry players and market end-users. The technologycan also be leveraged into other fabric or membrane applications, suchas water-treatment films, fuel cells in energy industries, and wounddress, hygiene clothes in health-care industries.

Example 2

The following example provides examples of fabrics of the presentdisclosure, characterization of same, methods of making same, and usesof same.

Personal moisture management fabrics that facilitate sweat transportaway from the skin is highly desirable for wearer's comfort andperformance. Demonstrated herein, for the first time, is a “skin-like”directional liquid transport fabric which enables continuous one-wayliquid flow through spatially distributed channels acting like “sweatingglands,” yet repels external liquid contaminants. The water transmissionrate was up to 15 times greater than that of best commercial breathablefabrics. This exceptional property is achieved by creating gradientwettability channels across a predominantly superhydrophobic substrate.The flow directionality is explained by the Gibbs pinning criterion. Inadditional to functional clothing, this concept can be extended todevelop materials for oil-water separation, wound dressing, geotechnicalengineering, flexible microfluidics and fuel cell membranes.

A fabric acts like a skin in directionally excreting water droplets andexpelling external liquid contaminants, with the water transmission ratebeing 15 times greater than that of best commercial breathable fabrics.

Described in this example is a conceptually novel design strategy thatbiomimetically mimics the behavior human skin. Human skin is a desirabledirectional liquid flow material as it excretes liquid sweat and protectthe body from external liquid contaminants (FIG. 4A). Herein, for thefirst time, a “skin-like” directional liquid transport fabric wasdeveloped, which allows continuous one-way water flow and repelsexternal liquid. This is achieved by endowing gradient wettability indistributed porous channels on a predominantly hydrophobic fabric. Weused a hydrophilic cotton fabric as a starting material, and pre-treatedit with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (PFOTES)-coatedtitanium dioxide (TiO₂) nanoparticles to impart superhydrophobicfinishing. Selective plasma treatment via a patterned mask was thenapplied to create the gradient wettability porous channels across thishydrophobic fabric (FIG. 4B), acting as localized sweat glands. Whilethese channels serve for one-way liquid flow, the predominantlysuperhydrophobic nature of the fabric makes it expel the transportedliquid or external liquid from the surface. This “skin-like” fabric hasgreat potentials to various applications such as functional clothing,oil-water separation, wound dressing, geotechnical engineering, flexiblemicrofluidics, fuel cell membranes, etc.

Firstly, the wetting behavior of the fabrics was checked before andafter superhydrophobic finishing and successive selective plasmatreatment. As shown in FIG. 5A, the superhydrophobic finished fabricshowed a contact angle (CA) of 152°, while that of the pristine cottonfabric is 0° (superhydrophilic, FIG. 8). The increased hydrophobicitywas caused by the surface nanostructures of the perfluorosilane-coatedtitanium dioxide nanoparticles. When the fabric was treated by theplasma etcher, the contact angles have a significant difference betweenexposed spot and unexposed non-spot areas. The CAs of the non-spot areason both top and back sides of the fabrics only decreased slightly andstill stayed at high values. This should be due to a complete coverageof the tape mask which prevents the 02 plasma going inside the fabricsand therefore less chance to endow hydrophilicity. On the contrary, theCAs of the exposed spot areas on both top and back sides of the fabricsdecreased dramatically with the increase of plasma treatment time. Forinstance, 1 min treatment brought the CA of the spot areas on the topside of the fabric down to 135°, which further decreased to 114° after 2min, 97° after 3 min, and 44° after 5 min, respectively. The CA changeof the spot areas on the back side of the fabrics was interesting, whichdropped down to 141° after 1 min, but was no longer measurable (N/A,noted as 0°) after 2 min or longer. This is because the water dropletstransported quickly from the back spot areas to the top spot areas (FIG.5A, inset images, and FIG. 8), therefore a zero CA values were recorded.A series of dynamic CA images can be found in FIG. 9 when 10 μL waterdroplet was placed on either side of the plasma (300 W, 3 min) treatedsuperhydrophobic finished fabric. When water was dripped onto theplasma-exposed top spot area, the droplet stayed on the surface steadilyfor 3 s and longer time (not shown), with an average CA of 97° (FIG.9A); however, when it was dripped on the reverse side (unexposed backspot area), the droplet quickly transported through to the other side(top side) of the fabric (FIG. 9B); for other non-spot areas on bothsides, the round water droplets kept still there (FIGS. 9C and 9D). Adynamic process of directional water transport can further be viewedwhere a 20 μL water is manually dripped from the pipette onto top andback spot areas of the fabric, respectively.

An initial guess for the reason of the water transport was that eitherdifferentiated wettability or wettability gradient occurred along thevertical direction of the spot areas through the fabric thickness. Toverify the cause, the “real” CAs of the spot areas on the back side ofthe fabrics need to be “measured”. To do this, two layers of thesuperhydrophobic finished fabric were assembled, then covered the topand back sides of the assembly with the patterned tape mask (FIG. 5B,inset image), and treated it with plasma. The CAs of the spot area weremeasured on the top side of the second layer and used it as the “real”CAs of the spot area on the back side of the first layer, with theassumption that they should be similar as the two layers are closelystuck. FIG. 5B shows that CAs decrease gradually along with the plasmaprolongation, but they are far over “zero”, e.g., 109° for the sampleafter 3 min plasma treatment. This means the plasma penetrates into thespot channels, and decreases the hydrophobicity to different degrees,therefore a wettability gradient should be formed through the fabricthickness. Notice, for the samples with less than 3 min treatment, bothtop and back spots are still hydrophobic (CA over 90°), whereas thesample with 5 min treatment turns to be hydrophilic on both sidesthrough the spot (also see FIG. 8). This may explain the hanging rounddroplet appearances for the transported water droplets on the opposite(top) side for the 2 and 3 min samples, and a spreading shape for the 5min sample, respectively (FIG. 5A, inset images, and FIG. 8). Thecontact angles of the plasma treated fabrics were also measured after 7days' aging at room temperature (FIG. 10A), and they showed the similartrends as those at Day 0 (FIG. 5A), indicating the samples were stable.In addition, the water transport time from the back spots to the topspots decreased with the plasma treatment prolongation, e.g. ˜5 s forthe as-prepared 2 min plasma treated fabric, about and below 1 s for the3 and 5 min samples, respectively; and the 7 days' samples only slightlyincreased the transport time at each corresponding condition (FIG. 10B).Overview images of multiple water droplets on either side of the treatedfabric at Day 0 and Day 7 can be found in FIG. 10C.

FIG. 5C shows the typical morphologies of the fabrics after differenttreatments. Compared with a smooth fiber structure on the pristinecotton fabric, the superhydrophobic finished fabric showed a rougherfiber surface because of the TiO₂ nanoparticles. The top spot area offabrics treated by plasma less than 3 min still kept woven fibrousstructure, but those treated more than 5 min generated fuzzy surfacesand broken fibers. The back spot areas have a similar morphology trendas the top area (FIG. 11), indicating plasma, besides the surfacetreatment on the top spot areas, can penetrate through the thickness viaspot channels and damage the fibers in different extents. All thenon-spot areas on both top and back sides did not change the initialfibrous morphologies (FIG. 12), because of a complete coverage by thetape mask. Combining the water transport screening by the contact angletest (FIG. 5A) and SEM morphologies (FIG. 5C), we chose thesuperhydrophobic fabric after selective plasma treatment under 300 W for3 min for further studies.

XPS was then used to investigate the chemical elements of the fabricsbefore and after superhydrophobic finishing and plasma treatment (300 W,3 min). As shown in the table of FIG. 5D, both the titanium (Ti) andfluorine (F) content increased after the TiO₂/PFOTES superhydrophobicfinishing on the cotton fabric. After selective plasma treatment, the Ticontent kept stable on both top and back spots, which coincides with theTGA data (FIG. 13) and identical rough morphology on the correspondingareas (FIG. 5C, FIGS. 11 and 12). However, there was a significantdifference in F content, which decreased from 34.53% to 0.91% and 15.36%on the exposed top and unexposed back spot areas, respectively. Thisindicates the fluorine-based hydrophobic silane chains on the exposedtop spot areas might be severely etched away by the plasma, and thoseunderneath the spots were also damaged by the penetration of the plasmathrough the thickness via spot channels, but in a less severe extent.Similar observations were previously reported. The indication of plasmapenetration coincides with the SEM trend (FIG. 5C) and contact angletrend either for the one layer (FIG. 5A) or two-layer structures (FIG.5B), and should be the reason for the gradient wettability andthereafter the directional water transport ability within the spotchannel area.

In order to confirm that the dual directional flow property and waterrepellency, the fabrics were placed at an incline angle of 45°, andwater was dripped from either top or back spot areas of the fabric by aneedle connecting with a continuous water source at a flow rate of 10μL/min. FIG. 6B shows a series of photos captured during theseexperiments. When water was dripped from top side of the fabric, itfirstly adhered to the spot area, e.g. first droplet at 5.0 s; duringthe continuous supply with water, the droplet grew and after the lastdroplet at 280.8 s, it was big enough (˜46 μL) to roll off from thefabric; through the entire process, no water transport was observed. Onthe reserve direction, when the first droplet contacted the back spotarea, it spontaneously transported from the pin of the needle to theother side after 10.0 s; and after accumulating to a similar volume at248.5 s, the large droplets roll off again from the top surface. Fromthis test, the maximum flow rate of each channel was estimated to be46/248.5=0.185 μL/s. In one of the test specimens, the spatial distanceof the channels is 1 cm, so the maximum water transport rate is0.185×0.001 g×3600/0.0001 m²/hr=6660 g/m²/hr, which far exceeds themaximum sweating rate of an average person under strenuous activity andis about 15 times greater than that of the best commercial Gore-Texfabric.

The breakthrough pressures of the top and back sides of the designedfabric having one spot were also experimentally examined via a waterflux test by placing a plastic hollow cylinder on either side to holdwater (FIG. 14A). The fabrics with different spot sizes at a flow rateof 0.4 mL/min were examined, as shown in FIG. 6B. Apparently, there aresignificant difference of the breakthrough pressures for the top andback sides of the fabric. For the top sides, the pressures were higherand decreased with the increase of the spot sizes, i.e. the smallestspot size (diameter) of 0.5 mm generated a 4.7 cm H₂O pressure, themedium size of 1 mm reduced the pressure to 3.76 cm H₂O, and the biggestsize of 3 mm further reduced to 1.8 cm H₂O. This is reasonable, as abigger plasma-exposed area would enlarge the channels for the water topass through, thereby lower breakthrough pressure. When the fabrics wereplaced inversely (back sides), the supplied water droplets can quicklytransport through, resulting a very low breakthrough pressure, ˜0.2 cmH₂O. The fabric with a spot size of 1 mm was tested at different flowrates, and it was found the pressure increased with the increase of thewater flow rates (FIG. 6C), which should be caused by the delay ofliquid penetration considering the predominantly flow resistance of thefabrics. In addition, the droplet sizes of the water transported throughthe spots were recorded and found they increased with the spotenlargement (FIG. 14B).

The directional water transport ability was further proved via anothertest by showering either top or back side of the fabric capping over aglass vessel loaded with blue silica gel beads (FIG. 15A). After thevessel being showered under an eye wash shower for 10 s, the color ofthe inside beads did not change when top side of the fabric was cappedupside (FIG. 15B), whereas it partially turned to pink when back sidewas capped upside (FIG. 15C), indicating a water transport through thefabric into the vessel.

Theoretical basis has been proposed to explain the design approach andunderstand the mechanisms of the directional water transport and therelease of water drops from the fabric surface. The dependence of theflow directionality and the breakthrough pressure on the microstructureand wettability of the fibrous systems has also been analyzed.

Water transport by liquid drops is much faster than that by vaporevaporation, while one water drops contains millions of vapor molecules.The underlying principle of the fluid directionality in the porous spotwith gradient wettability is illustrated in FIG. 7A. Here, the Gibbspinning criterion, which has been successfully correlated to the flowdirectionality in the fibrous fluid diodes with varied geometry, isextended to describe the directional water transport inside the hollowchannels between yarns with both gradient wettability and variedmicrostructure. Since the channel between the yarns varies in size alongthe flow direction, an expansion/contraction angle (α) is used tocharacterize the degree of the expansion or contraction of flow path(FIG. 7B). When the channel is uniform in size, a becomes zero. And aapproaches 90° or −90°, respectively, at the bottom and the top of thefibrous material in the flow direction. More specifically, the contactline gets pinned with the breakthrough angle α+θ beyond 90° based on theGibbs pinning condition. On the contrary, the advancement of the liquidcontinues when the air-liquid interface is concave and the draggingforce exists towards the flow direction. As such, continuous advancementof the liquid water can be satisfied, when the direction angle as afunction of contact angle θ and the expansion/contraction angle α issatisfied as follows,

$\begin{matrix}{{\beta = {{\alpha + \theta - \frac{\pi}{2}} < 0}},} & (1)\end{matrix}$

It can also be seen from FIG. 7B that liquid water will flow inverselyif β>0, as the driving force on the basis of surface tension becomesopposite to the intended flow direction. Assume the yarns areelliptical, their surface can be described as the locus of all pointsthat satisfy the equations, viz., x=a cos ω, and y=b sin ω, where x andy are the coordinates of any point on the ellipse, a and b are thesemi-axes in the x- and y-directions, respectively, ω is the angle ofeccentric anomaly, which ranges from π/2 to −π/2 radians in FIG. 7B. Thevalue of a can be determined by the slope of the tangent line at (a cosω, b sin ω) to the ellipse, viz., α=arctan

$\left( \frac{1}{k} \right),$

where

$k = {{- \frac{b}{a}}{\frac{\cos \mspace{11mu} \omega}{\sin \mspace{11mu} \omega}.}}$

It has been shown in FIG. 5B that the bottom surface (back side) of theporous spot becomes less hydrophobic with increasing time of plasmatreatment. Here, a linear gradient of wettability is assumed from thehydrophilic (simplified as ‘I’) top spot surface with contact angle at0° when ω=π/2 to the hydrophobic (simplified as ‘O’) bottom surface withcontact angle at θ₀ when ω=−π/2, with

$\theta = {\theta_{IO} = {{{- \frac{\theta_{0}}{2}}\sin \mspace{11mu} \omega} + {\frac{\theta_{0}}{2}.}}}$

In the opposite flow direction, the contact angles will be

$\theta_{IO} = {{\frac{\theta_{0}}{2}\sin \mspace{11mu} \omega} + \frac{\theta_{0}}{2}}$

with contact angle at 0° when ω=−π/2 to the bottom surface with contactangle at θ₀ when ω=π/2. The maximum value of the contact angle on theface away from plasma exposure is obtained as θ₀=109° for the samplewith 3-min treatment (FIG. 5B). The dependence of the diode effect on cothat indicates the water advancement is shown in FIG. 7A, where the sign“block” indicates the flow ceases or retreats at the local area whilethe sign “pass” means that the flow can continue moving. It is foundthat the values of a and b in Eq. (1) are approximately 80 μm and 50 μm,and c is approximately 50 μm, respectively (FIG. 16). Note that thesurface tension force is always aligned with the flow direction at β<0,when the water flows from the hydrophobic side to the hydrophilic sideas seen in FIG. 7C. It can be readily understood that the effect ofdramatic contraction leading to high α (negative) overcomes that of thefair hydrophobicity with θ_(OI)>90° at the beginning stage and in therest of flow process, while the condition of β<0 is always satisfiedwith the reduction of θ_(OI). In the adverse flow direction, thecondition of β<0 is also secured at the beginning with α<0 and θ_(IO)˜0.However, β eventually becomes positive and the surface tension force isopposite to the main flow direction, with continuously increasing a(positive) and θ_(IO) during the progress of water movement. As such,the asymmetric flow behaviors from different flow directions result fromthe changes of the geometrical structures and gradient wettability ofthe fibrous systems, as revealed by the theoretical model of Eq. (1) andexperimental findings in FIG. 6. The dependence of direction angle oneccentric anomaly of the elliptical yarns in different flow directionshas been further studied in FIG. 17, when the semi-major axis andsemi-minor axis vary at different values of the maximum contact anglesof one surface of the porous spot (i.e., θ₀=109° and θ₀=170°). It isinteresting to note that both flows can be hindered from two differentdirections for θ₀=170° when b=80 μm and α=50 μm, because the contactangle of the yarn surface is always high in a wide area, where theexpansion/contraction angles keep close to zero.

The detachment of water drops is essential to the continual directionalwater transport process. In this work, patterned hydrophilic porousspots are distributed on the predominantly superhydrophobic surface foreasy water removal. The size and wettability of the spots are related tothe breakthrough pressure and detachment of water drops. It is notedthat the capillary pressure varies at different positions of fluidfronts, and the maximum value of capillary pressure that blocks thewater transport will be equal to the breakthrough pressure when thegravitation force is negligible. The capillary pressure within thechannel between yarns is determined by the Young-Laplace equation,

$\begin{matrix}{p = \frac{\gamma \; {\sin \left( {\alpha + \theta - \frac{\pi}{2}} \right)}}{L}} & (2)\end{matrix}$

where L=a+c−a cos ω is the half distance of the width of the fluid frontand c is the half distance between yarns. It is clear that the capillarypressure is all negative in the OL flow direction in FIG. 7D (and FIG.18A), so the breakthrough pressure will be equal to zero consistentlywith the advance of the liquid water. From the opposite flow direction,a positive capillary pressure is found with the maximum value at 800 Pa(8.16 cm water head). This capillary pressure is greater than the 3.76cm water head shown in FIG. 6B, possibly because some porous spotscontain larger channels with greater c (see arrow in FIG. 16B), leadingto the reduction in capillary pressure. With increasing a while keepingb and c as constants, FIG. 18B reveals that a flatter shape ofelliptical yarn can yield a lower breakthrough pressure. Besides, morehydrophobic porous spots with higher θ₀ leads to an increase inbreakthrough pressures, as seen in FIG. 18C.

With increasing water supply, the volume of water drops increases untilthey fall off from the porous spot with the gravitational forceovercoming the surface tension. The contacting circle interface lineamong the air, the water drop and the fabric cannot enlarge due to therepellence of the surrounding hydrophobic regions (FIG. 7E). Thus thecorresponding surface tension drag is equal to F_(a)=2πrσ sin θ, where ris the radius of the hydrophilic porous spot and θ<90°. Then the dragwill be balanced with the critical gravitational force of the growingwater drop, which has a weight of G=μg(4πR³/3). Thus the scaling law isaccounting for the relationship between r and R based on F_(a)=G, viz.,

r˜R³  (3)

which holds until the detachment of the water drops. Eq. (3) has beenwell verified by the experimental results of detachment of water dropsat different sizes of porous spots (FIG. 7F, also see FIG. 14B).

When the fibrous layer is placed at an incline angle at λ=45°, thesurface tension drag is generated by the hydrophilic and hydrophobicareas, F_(a)=πγR_(f)(cos θ_(r)−cos θ_(a)), where θ_(a) and θ_(r) are theadvancing and receding contact angle, respectively (FIG. 7G). Thehydrophilic force in the upper area of the porous spot holds the waterdrop and the hydrophobic force in the lower region repels and impedesthe water drop from rolling off. The gravitation force of the water dropis scaling to mg sin λ, which will be equal to the capillary forces atthe detachment condition, viz.,

mgsin λ˜πγR_(f)(cos θ_(r)−cos θ_(a))  (4)

where the mass of water drop scales with the cubic drop radius R_(f),viz., m˜R_(f) ³. Analogous to the phenomenon described in Eq. (3), theincrease in m is much faster than that of R_(f) in Eq. (4), whichexplains the detachment of growing water eventually drops. Thedirectional water transport will stop if the Laplace pressure of thesupplied water drop is equal to the hydrostatic pressure of the watercolumn or water drop generated in the other side of the fabric. However,this condition cannot be met in reality as the water drop will fall offwhen growing slightly big.

In summary, described herein is a novel “skin-like” fabric with bothdirectional water transport and water repellency. Distributed porousspot channels with gradient wettability across the thickness ofhydrophobic fabrics via a combination of superhydrophobic finishing andselective plasma treatment were created. While these channels serve fordirectional liquid transport, the predominantly untreated surface arearemained superhydrophobic, therefore repels external liquidcontaminants. The mechanism of directional flow is explained by theGibbs pinning criterion. The technology might be applicable for allkinds of fabrics. Either the hydrophobic pre-finishing or selectiveplasma treatment is simple and efficient, therefore will be veryfeasible for the commercial applications. The proposed fibrous materialscan have a direct application in developing smart and high performanceclothing, especially for sportswear. It has a high significance to theapparel industry, for bringing both directional water transport propertyand water repellency, therefore would bring a huge value for theindustry players and market end-users. The technology can also beleveraged into other fabric or membrane applications, such as liquidseparation and purification, fuel cells, wound dressing, and flexiblemicrofluidic devices.

Materials and Methods. Superhydrophobic finishing of cotton fabrics. Thefabrics used for the experiment were woven cotton fabrics. They weretreated via conventional desizing, scouring, and bleaching process priorto the use.

The superhydrophobic coating was prepared using the following protocol.2.0 g 1H, 1H, 2H, 2H-Perfluorooctyltriethoxysilane (C₁₄H₁₉F₁₃O₃Si, 97%,Oakwood) (noted as PFOTES) was dissolved in 198 g ethanol via vigorousmixing for 2 hours. The solution was subsequently mixed with 10 gDegussa P25 titanium dioxide nanoparticles (TiO₂, Rutile: Anatase/85:15,99.9%, 20 nm; Degussa) to form a suspension. The cotton fabrics withdesigned sizes were immersed in the coating suspension for 5 min, anddried in air for 10 min before testing.

Selective plasma treatment of the finished fabrics. One side of thesuperhydrophobic finished cotton fabric (notated as top side) wastightly covered by a layer of paper tape mask with laser-cut holepatterns (diameter varies from 0.5 to 3 mm, with a typical one of 1 mm,the intervals between holes is 10 mm), another side (notated as backside) was covered by the same tape mask without the hole patterns (FIG.3B). The masked fabric was placed into an oxygen gas plasma etcher(PE100RIE, Plasma Etch Inc.) and treated under 02 flow rate of 50 cc/minand power of 300 W, for a certain time. Because of the patterned mask,only the hole spot area of the top side of the fabric was expected to beexposed to the plasma. After plasma treatment, the tape mask was peeledoff from both sides of the fabric.

Characterization

Contact Angle Measurement:

Contact angles (CA) of the fabrics were measured via the sessile dropmethod using a Movie Contact Angle (VCA) System (AST Products,Billerica, Mass.) equipped with the software (VCA Optima XE). Thefabrics were cut into strips, and hung in the air by fixing two endsusing a thick (˜8 mm) epoxy putty tape on a glass slide. A 10 μL waterdroplet was placed on the fabric surface to check either its contactangle or the transport properties. At least five parallel measurementsfrom both spot and non-spot areas on both sides of the fabrics wereconducted on each specimen, and the results of either contact angles ortransport time were averaged for each fabric sample.

Morphology Analysis:

Scanning electron microscopy (SEM, Tescan Mira3 FESEM) was used to studythe microstructure of the cotton fabric before and aftersuperhydrophobic and plasma selective treatments. The samples werecoated with a thin layer of gold palladium before observation.

Chemical Analysis:

The surface chemical information of the cotton fabrics before and aftersuperhydrophobic finishing and plasma treatment were analyzed usingX-ray photoelectron spectroscopy (XPS) (SSX-100, Surface ScienceInstruments) with operating pressure of ˜2×10⁻⁹ Torr. Monochromatic AlKα x rays (1486.6 eV) with 1 mm diameter beam size was used.Photoelectrons were collected at a 55° emission angle. Electron kineticenergy was determined by a hemispherical analyzer using a pass energy of150 V for wide/survey scans ranging from 0 to 1100 eV. A flood gun wasused for charge neutralization of all the samples. The data analysis wasperformed on CasaXPS software.

Thermal Analysis:

A thermogravimetric analyzer (TGA 500, TA Instruments) was used todetermine the amount of TiO₂ nanoparticles deposited on the treatedfabric. 5-10 mg of each sample was placed in an alumina ceramicscrucible and thermally heated from 30 to 990° C. in a nitrogen gasmedium with a heating rate of 10° C./min. The weight percentage of TiO₂nanoparticles was estimated by calculating the difference between theremaining weight of pristine cotton fabric and TiO₂/PFOTES-coatedfabric.

Water Dripping Test:

Water droplets of ˜20 μL per droplet were dripped onto either top orback sides of the horizontally laid superhydrophobic finished fabricsafter selective plasma treatment. Continuous water droplet supplied froma syringe pump (SK-500 III, Shenzhen Shenke Medical, China) with a flowrate of 10 μL/min was dripped by a needle on either top or back sides ofthe 45° inclinedly laid fabrics.

Water Flux Test:

A home-made device was set-up to measure the breakthrough pressure ofthe fabrics (FIG. 14A). The device includes a water source from asyringe pump, a hollow syringe cylinder with the bottom end attachedwith the testing fabric and an underneath glass bottle collector. Duringthe test, the fluid rate was set as 0.05, 0.09, 0.4 and 0.95 mL/min,respectively. The breakthrough pressure was recorded as the minimumpressure under which the water starts to pass through the fabric.

Water shower test: The water transport properties were further measuredby a water shower test. A testing fabric was capped over on a 20 mLglass vessel loaded with ˜1 g blue silica gel beads. The vessel was thenshowered by an eye shower for 10 s, and the color of inside silica gelbeads was checked to find whether there was water transported throughthe fabric. Both top and back sides of the fabrics were tested to checkthe transport difference.

Although the present disclosure has been described with respect to oneor more particular embodiments and/or examples, it will be understoodthat other embodiments and/or examples of the present disclosure may bemade without departing from the scope of the present disclosure.

1. A fabric exhibiting directional liquid transport comprising aplurality of domains, each of the domains connecting a first side of thefabric and a second side of the fabric opposite the first side, whereineach of the domains has a gradient in concentration of hydrophobicand/or oleophobic groups and, optionally, a plurality of nanoparticlesdisposed on a fabric surface.
 2. The fabric of claim 1, wherein theplurality of domains comprise 0.1-75 wt % of the surface area of thefabric and the hydrophobic and/or oleophobic groups comprise 1-75 wt %of the fabric.
 3. The fabric of claim 1, wherein each of the domains ischaracterized by a gradient in hydrophilicity and/or oleophobicity alonga direction from the first side of the fabric to the second side of thefabric.
 4. The fabric of claim 1, wherein the hydrophobic and/oroleophobic groups are fluoroalkyl groups, alkyl groups, silsesquioxanegroups, siloxane groups, or a combination thereof, and the hydrophobicand/or oleophobic groups are covalently bound to a surface of one ormore nanoparticles of the plurality of nanoparticles.
 5. The fabric ofclaim 1, wherein the hydrophobic and/or oleophobic groups are connectedto the fabric surface via one or more covalent bonds.
 6. The fabric ofclaim 1, wherein the plurality of nanoparticles are chosen from titaniananoparticles, silica nanoparticles, zinc oxide nanoparticles, carbonnanoparticles, and combinations thereof.
 7. The fabric of claim 1,wherein the individual domains of the plurality of domains have a roundshape, rectangular shape, oval shape, kidney shape, triangular shape,star shape, or a combination thereof.
 8. The fabric of claim 1, whereineach of the domains has a size of 100 microns to 5 mm, wherein each ofthe domains has the same size or each of the domains has a differentsize.
 9. The fabric of claim 1, wherein the fabric comprises naturalfibers, synthetic fibers, semi-synthetic fibers, or a combinationthereof.
 10. The fabric of claim 1, wherein the fabric is a knittedfabric, a woven fabric, a non-woven fabric, or a combination thereof.11. An article of manufacture comprising one or more fabric of claim 1.12. The article of manufacture of claim 11, wherein the article ofmanufacture is a wearable article or an outdoor article.
 13. The articleof manufacture of claim 12, wherein the wearable article is chosen fromrainwear, outerwear, outdoor clothing, sportswear, skiwear, hiking wear,under garments, socks, t-shirts, hats, gloves, mittens, jackets, coats,and ponchos.
 14. The article of manufacture of claim 12, wherein theoutdoor article is chosen from tents, awnings, tarps, and sleeping bags.15. A method of forming a fabric exhibiting directional liquidtransport, comprising: exposing selected areas of a superhydrophobicand/or oleophobic fabric to an oxygen or air plasma, such that one ormore domains exhibiting a water and/or oil transport gradient from afirst side of the fabric to a second side of the fabric opposite thefirst side of the fabric are formed, wherein a superhydrophobic and/oroleophobic fabric exhibiting directional liquid transport is formed. 16.The method of claim 15, wherein the fabric has a hydrophobic and/oroleophobic coating.
 17. The method of claim 15, wherein thesuperhydrophobic and/or oleophobic fabric is formed by: contacting afabric or a portion thereof with: one or more hydrophobic groupprecursors and/or one or more oleophobic group precursors, optionally, aplurality of nanoparticles, and optionally, a solvent wherein thesuperhydrophobic and/or oleophobic fabric is formed.
 18. The method ofclaim 17, wherein the one or more hydrophobic group precursors and/orone or more oleophobic group precursors, optionally the plurality ofnanoparticles, and optionally the solvent are present as a preformedmixture.
 19. The method of claim 17, wherein the hydrophobic groupprecursors and/or oleophobic group precursors are 1-100 wt % of thefabric.
 20. The method of claim 17, wherein the hydrophobic groupprecursor is chosen from fluoroalkyltrialkoxysilanes, silsesquioxanes,polydimethylsiloxanes (PDMSs), polyolefins, waxes, and combinationsthereof.
 21. The method of claim 20, wherein thefluoroalkyltrialkoxysilane is chosen from¹H,¹H,²H,²H-perfluorooctyltriethoxysilane (PFOTES),¹H,¹H,²H,²H-perfluorodecyltrichlorosilane (PFTDS),¹H,¹H-perfluorooctylamine (PFOTA), perfluorooctylated quaternaryammonium silane coupling agent (PFSC),¹H,¹H,²H,²H-perfluorooctyltrichlorosilane (PFOTS),poly(tetrafluoroethylene) (PTFE),¹H,¹H,²H,²H-perfluorodecyltrichlorosilane (PFODS),¹H,¹H,²H-perfluoro-1-dodecene (PFDDE),(heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane (FDTS),perfluoroalkyl methacrylic copolymer (PMC), and combinations thereof.22. The method of claim 17, wherein the plurality of nanoparticles arechosen from titania nanoparticles, silica nanoparticles, zinc oxidenanoparticles, carbon nanoparticles, and combinations thereof.
 23. Themethod of claim 15, wherein the exposing selected areas of thesuperhydrophobic and/or oleophobic fabric to an oxygen or air plasma isperformed utilizing a masking material having a plurality of apertures,wherein the apertures correspond to the selected areas.